RTL files are now created on build for core CSS files. These files replace the LTR file completely, rather than being in addition to the existing LTR file.
Benefits:
* For the user: less CSS is served in RTL, less HTTP requests on the frontend, and less work for the browser.
* For the core developer: Let the tools do the work.
Notes for core development:
* The file generation task is `grunt rtl`.
* `grunt watch` now handles generating RTL files in /build when a CSS file in /src is saved.
* /src is now locked to LTR. RTL testing must occur via /build. When attempting to run an RTL text direction with /src, an admin notice will display.
Expect RTL bugs. Please report them.
props yoavf.
see #24977.
Built from https://develop.svn.wordpress.org/trunk@26107
git-svn-id: http://core.svn.wordpress.org/trunk@26022 1a063a9b-81f0-0310-95a4-ce76da25c4cd
